tire size question

[eandsphotography]

My 05 dodge ram 1500 came with the 20 inch wheels and tires. I was wondering if I put 17's on it if it would give me more towing capacity and if so do you think it would be a noticable difference?
any suggestions??

[Radio]

The Ford F-150 "Harley-Davidson" edition comes with fancy 20" wheels and the towing/payload capacity is reduced vs the standard F-150. Part of payload is the amount of weight the tires will handle. So yeah, I guess regular wheels with good tires will help, but then how would you calculate that??

[moorer2]

This may help you calculate what you are looking for.

[eandsphotography]

thanks for that equation but i'm a little confused on it. I know i have a 3.92 rear end and if i take the 17 and divide it by 20 x 3.92 that comes out to be 3.332 ; That cant be right can it? that would give me less rear end ratio.
if i do it the other way 20 divide by 17 x 3.92 then that comes out to be 4.61 which seems like that would be correct in giving more gear ratio.
Ok who here hates fractions!!!!

[Radio]

Not the rim diameter, the tire diameter. The 17" rims should carry a taller sidewall. The whole point of the 20" rim is to fit a "sporty" looking low profile tire.

And then what is this going to do to your speedometer reading?

[moorer2]

Yeah. I hate fractions. Try this site and just plug in the numbers. This should help you with gear ratio and speedometer adjustments. Also, if you use a gps, it will give you your speed to check against your trucks speedo.
http://www.csgnetwork.com/multirpmtirecalc.html

[Bama Rambler]

When Dodge put the 20" rims and tires on the 1500 they upped the gear ratio to 3.92 to compensate for it so it didn't affect tow rating.

Now as Radio says it's ultimately the tire diameter difference that's going to affect your rating. If the tire diameter reduces in tandem with the rim diameter then IMHO you'll gain about 1000 to 1500 lbs of towing capacity.

According to the Dodge towing site they increase towing capacity by 1000 lbs for approx every .4 increase in axle ratio.

This is just my opinion and in no way is to be taken as fact. I also didn't take into account any other info such as frame stength, springs, axle, etc.

Your Dodge dealer should be able to reprogram your ECM to correct your speedo once you've gotten the tires on it.

[Radio]

What i'd like to know is, will a slightly larger tire improve my fuel economy?? Wonder where a calculator is for that??